Regional Movements of Reef Manta Rays (Mobula alfredi) in Seychelles Waters

Abstract

The decline in numbers of reef manta rays (Mobula alfredi) throughout their range has highlighted the need for improved information on their spatial ecology in order to design effective conservation strategies for vulnerable populations. To understand their patterns of movement in Seychelles, we used three techniques-archival pop-up satellite tags, acoustic tags, and photo-identification-and focussed on the aggregation at D'Arros Island and St. Joseph Atoll within the Amirantes Group. M. alfredi were photographed within six of the seven Island Groups of Seychelles, with 64% of individuals being resighted at least once between July 2006 and December 2019 over timeframes of 1-3,462 days (9.5 years; median = 1,018 days). Only three individuals from D'Arros Island were resighted at a second aggregation site located more than 200 km away at St. François Atoll during photo-identification surveys. Satellite-tracked M. alfredi (n = 5 tracks; maximum 180 days) remained within the boundary of the Seychelles Exclusive Economic Zone, where they spent the majority of their time (87%) in the upper 50 m of the water column in close proximity to the Amirantes Bank. The inclusion of acoustic tagging data in the models of estimated satellite-track paths significantly reduced the errors associated with the geolocation positions derived from archived light level data. The insights gained into the patterns of horizontal and vertical movements of M. alfredi using this multi-technique approach highlight the significance of D'Arros Island and St. Joseph Atoll, and the wider Amirantes Group, to M. alfredi in Seychelles, and will benefit future conservation efforts for this species within Seychelles and the broader Western Indian Ocean.

Reverse diel vertical movements of oceanic manta rays off the northern coast of Peru and implications for conservation

“…For example, basking sharks tracked in the English Channel displayed patterns of normal DVM in deep, well-stratified waters and reverse DVM in shallow, inner-shelf areas near thermal fronts, with such changes in behaviour between habitats likely mimicking those of zooplankton (Sims et al, 2005). Similarly, locational differences in DVM patterns have been recorded by reef manta rays, with normal DVM recorded around the islands and atolls of the Chagos archipelago (Andrzejaczek et al, 2020), and reverse DVM in both the coastal and offshore areas of the Red Sea (Braun et al, 2014), and the islands and atolls of Seychelles (Peel et al, 2020). Such diversity in foraging modes enables flexibility as these animals encounter spatial and/or temporal changes in the zooplanktonic prey community.…”

First insights into the vertical habitat use of the whitespotted eagle ray Aetobatus narinari revealed by pop‐up satellite archival tags

“…To better resolve horizontal movement patterns, future studies could combine passive acoustic telemetry with PSAT technology. Inclusion of acoustic tagging data can reduce the error associated with geolocation estimates (Peel et al ., 2020) and provide insight into more fine‐scale horizontal movement patterns. Future studies should focus on expanding tagging efforts further south in the Gulf of Mexico and the Caribbean.…”

“…For example, research on the reef manta ray Manta alfredi (Krefft 1868), a planktivorous coastal‐pelagic batoid, indicates that patterns of vertical movement vary by location. M. alfredi in the British Indian Ocean Territory exhibit diel vertical migration (DVM), occupying deeper mean diving depths during the day and moving up through the water column at night (Andrzejaczek et al ., 2019), whilst in the Red Sea and around the Seychelles M. alfredi remain closer to the surface during the day and dive deeper at night (Braun et al ., 2014; Peel et al ., 2020), a movement pattern known as reverse DVM. Both vertical movement strategies may be driven by foraging behaviour, with the contrasting patterns being attributed to regional oceanography affecting the distribution of their prey (Andrzejaczek et al ., 2020).…”

“…Temperature has been coined the “ecological master factor” that affects the physiology of aquatic ectotherms and consequently many fish, including the bat ray Myliobatis californica Gill 1865, behaviourally thermoregulate (Brett, 1971; Matern et al ., 2000). Lunar phase, due to its relationship with tides, illumination and changes in predator–prey distribution, has also been shown to influence the depth and habitat use of several elasmobranch species (Braun et al ., 2014; Dewar et al ., 2008; Vianna et al ., 2013; Whitty et al ., 2017), including M. alfredi (Braun et al ., 2014; Peel et al ., 2020). Additional investigation into the vertical movement of batoids and the reasons for these movements could shed light on potential interactions between species and trophic dynamics (Vaudo et al ., 2014).…”

Behavior and Ecology of Silky Sharks Around the Chagos Archipelago and Evidence of Indian Ocean Wide Movement

“…For individuals tagged with MiniPATs, location estimates were processed using the manufacturer's software, Geolocation Processing Estimator 3 (GPE3; Wildlife Computers Inc., Redmond, WA, United States), which has been used widely to process elasmobranch tracking data (e.g., Skomal et al, 2017;Hutchinson et al, 2019;Peel et al, 2020). GPE3 generates two maximum likelihood position estimates per day using a hidden Markov model (Patterson et al, 2009) with a 0.25 • × 0.25 • grid spacing, and position estimates (two per day) interpolated and smoothed with a cubic spline.…”